The present invention relates to a shearer for use in coal or metal mining and suitable for effecting the long wall mining method. More particularly, the present invention relates to a shearer provided with a device for detecting the position of a lower cutting drum according to the height which the long wall face of a coal or metal mine is cut by another upper cutting drum to always keep the mining height constant.
Ranging drum shearers are well known as conventional coal mining machines and the shearers of this kind can be divided into two groups, one of which is a single ranging drum shearer provided with a ranging arm only at one end of the shearer having a cutting drum, while the other is a double ranging drum shearer provided with ranging arms at both ends of the shearer having cutting drums.
Since the single ranging drum shearer has only one cutting drum, generally speaking, it is difficult to cut the whole height of the seam by one pass of said shearer. Accordingly, it is necessary to reciprocate the shearer along the pit face changing the height of the shearer every travel along the pit face.
On the other hand, the double ranging drum shearer has ranging arms provided at the front and back ends of shearer, each ranging arm having one cutting drum. Therefore, the preceding drum is positioned high to function as a drum for cutting the pit face at the side of the mine roof and the other succeeding drum is positioned low to function as another drum for cutting the pit face at the side of the mine floor, thus enabling the shearer to cut the entire seam height at one time.
In order to cut the pit face using the double ranging drum shearer, the operator must judge by himself whether or not the cutting operation is correct by viewing the top of cutting drum arranged at the side of the mine roof and the bottom of another cutting drum arranged at the side of the mine floor. The cutting operation of the drum arranged at the side of the mine roof provides no problem since the top of the drum can be easily viewed. However, the cutting operation of another drum arranged at the side of the mine floor depends on the skill of the operator since the bottom of the drum cannot be easily viewed because of the presence of coal previously cut by the preceding cutting drum and scattered on the mine floor and also because of the presence of a conveyor arranged on the mine floor along the pit face. Therefore, when the shearer is operated by an unskilled operator, the mine floor is either made uneven, having wave-formed concave-convex portions, or the distance between the mine roof and floor, i.e., the mining height, is exceeded by the maximum height of self-advancing supports or made lower than the minimum height of self-advancing supports, so that the working operation at the pit face is hindered and the mining efficiency is lowered.
In order to overcome the above-mentioned drawbacks, the inventors of present invention previously disclosed a new technique in their publicly opened Japanese Pat. No. 958,841. This technique comprises attaching a sensor to the head of a ranging arm of a cutting drum arranged at the side of the mine roof, said sensor to use the change in the elasticity of spring or oil pressure by the pantograph or diaphragm manner and arranged to contact and follow the mine roof surface to detect the change in the shape of the mine roof surface. Accordingly, the other cutting drum arranged at the side of the mine floor is raised or lowered responding to the signals transmitted from the sensor to thereby keep the mining height constant. However, according to this technique, the succeeding lower cutting drum is raised or lowered responding to the changes in the mine roof height detected by the sensor arranged to the preceding upper cutting drum, and the mining height is therefore not maintained accurately, because the preceding and succeeding cutting drums are arranged at both ends of the shearer body with a certain space interposed therebetween and the succeeding lower cutting drum is raised or lowered instantly responding to the information detected by the sensor which is arranged to the upper cutting drum preceding several meters ahead of the succeeding lower cutting drum. In addition, the sensor is affixed to the head of the ranging arm. Therefore, when the ranging arm is raised or lowered, the sensor is also raised or lowered at the same time, so that the sensor is slanted causing the measurement made by this slanted sensor to have errors. Further, the sensor employed by this technique is arranged to contact and follow the mine roof surface. However, it is difficult to cause the sensor to contact and follow the concave-convex surface of the mine roof accurately. In addition, an accident is easily happen in this case.